We propose a series of experiments that are directed toward determination of the molecular basis of cell adhesion in embryonic cells and in transformed cells. Our approach is to attempt to isolate phases of the adhesion process and to determine the components and the processes involved. We have operationally divided adhesion into two phases: an initial contact phase and a phase during which increased stability occurs. The initial contact phase is analyzed quantitatively by an aggregate collection assay where it is possible to follow kinetically the collection of a population of cells to aggregates. Stability is measured quantitatively by a resistance to loss of adhesion through increased shear. Our studies will combine the use of inhibitors, antisera, and isolated cell components to define how cell interactions occur. We will rely heavily on the observation that freshly trypsinized cells are not adhesive but become adhesive after a period of recovery. We will use this observation to determine what molecules must be replaced in order to restore adhesiveness. To study the initial adhesive interactions of recovered cells we will rely on the observation that collection of a population of recovered cells occurs at a linear rate. This rate can be used to determine whether agents that affect adhesion do so directly (competitively) or indirectly.